Zinc calcine for hydrometallurgical process



May 4, 1965 M. J. BRoQKs E-rAl. 3,181-,944

ZINC CALCINE FOR HYDROMETALLURGICAL PROCESS Filed May '7 all.

United States Patent O Fice 3,ll,944 ZHNC CAlLClNE FR HYDRMETALLURGICALPROCESS Maxwell il. Brooks, New York, NX., and Robert l. Newman,Allendale, NJ., assignors to Allied Chemical Corporation, New York, NX.,a corporation of New York Filed May 7, i962, Ser. No. 192,661 4 Claims.(Cl. 7S9) This invention relates to the oxidation and desulphurizationof Zinc sulfide ores and more particularly refers to a new and improvedprocess for calcining zinc sulfide concentrates with high iron contentto produce a zinc calcine for hydrometallurgical treatment andconcomitantly high strength SO2 gas for conversion into H2804.

Zinc sulfide ores used for production of metallic zinc are usuallyflotation concentrates which are finely ground to free the individualore from gangue particles. The zinc content will range from about 45-55%and sulfur from 27-36% with iron present in quantities ranging fromabout 1% to 15%. The roasted zinc oxide, usually termed calcine, isemployed to convert it to Zinc metal by two distinct methods (a)pyrometallurgical process and (b) hydrometallurgical process. If thecalcine is to be converted by a pyrometallurgical process such as retortdistillation, the quality of the roasted zinc oxide is usually not ascritical. Fine calcine is usually agglomerated or sintered prior toretorting and residual sulfur content of calcine, which can supply aportion of the fuel, is eliminated during sintering. Furthermore,soluble zinc co-ntent of calcine is of no concern in pyrometallurgicaloperations.

ln hydrometallurgical processes, calcine quality is of major importanceand maximum solubility of the zinc content of the calcine in leachliquor is essential. Small increases in solubility of the calcine inleach liquor has a profound effect on the efficiency and economics ofthe processan increase in solubility of 2% may reflect a saving of aquarter of a million dollars a year for a zinc plant of average size. lnaddition certain impurities normally produced in roasting materiallyreduce the yield and hamper and complicate the electrolytic refining.From the foregoing it will be evident that the quality of the calcineproduced by roasting has an important bearing on the subsequentconversion of the calcine by hydrometallurgical process. The presentinvention is particularly directed to producing a calcine suitable forhydrometallurgical refining and processes requiring a high qualitycalcine product.

An object of the present invention is to provide an efficient processfor calcining Zinc sulfide ores containing iron to produce sulfurdioxide and calcine eminently suitable for conversion to metallic zincby hydrometallurgical process. Another object of the present inventionis to provide a process for roasting iron Zinc concentrates to produce acalcine with lower sulfide and sulfate sulfur and at the same timehigher soluble zinc. Other objects and advantages will be apparent fromthe following description and accompanying drawing.

in hydrometallurgical processes for production of metallic zinc, zinccalcine is leached with leach liquor which is an aqueous solution ofsulfuric acid, the latter reacting with the zinc oxide in the calcine toform zinc sulfate. This liquor is then subjected t electrolysis todeposit zinc metal and form sulfuric acid which latter is recirculatedas leach liquor for leaching additional zinc calcine. The quality ofzinc calcine for hydrometallurgical process is most important to thesuccess of the operation. The quality of calcine is determined by (a)concentration of Zinc sulfide (ZnS), (b) concentration of Zinc sulfate(ZnSO4), (c) concentration of ferrite (2110.136203) which factors inturn materially affect the solubility of Zinc con- 3,l8l,9l-d PatentedMay 4, i965 tent of the calcine in leach liquor. Zinc sulfide in thecalcine is insoluble in the leach liquor and represents a yield loss. Inpractice the maximum amount of zinc sulfide in the calcine consideredtolerable is 0.6 percent and of course any reduction in zinc sulfidebelow this maximum value represents material gain. Zinc sulfate issoluble in the leach liquor, but, the ratio of zinc oxide to sulfate inthe calcine is limited by requirements of the leaching and electrolyticcircuits. Should the sulfate content of the calcine exceed a limit ofabout 2.0 percent, purging of the leach liquor will be required, alsoentailing a loss in zinc yield. A further complication is introduced bythe presence of iron in the ore feed. Zinc oxide and ferrie oxide inintimate contact react to form acid insoluble zinc ferrites (ZnO.Fe2O3).The loss in Zinc due to insoluble zinc ferrites is represented in theindustry as the ferritization ratio defined as the Weight of zincrendered insoluble oy a unit weight of iron. To illustrate these valuesreference is made to the article Suspension Roasting of ZincConcentrates by R. E. Eyre, page 592, Canadian Mining & MetallurgicalBulletin, vol. 54, No. 592, August 1961, wherein the ferritization ratioof prior art method is given as 0.522 and emphasis is placed on the factthat the author reports on an operation which succeeded in reducing theferritization ratio to 0.46. Obviously a process which obtains evenfurther reduction in the ferritization ratio represents a markedimprovement in the art. From the foregoing it will be evident that thequality of Zinc calcine for use in hydrometallurgical processes iscomplicated by several factors and reflects itself materially in theoperation of the hydrornetallurgical process,

Roasting of sulfide ores is an old art and in fact roasting of ore in afluidized bed with entrainment of fines was disclosed more than S0 yearsago. However roasting of zinc sulfide ores containing iron for use inhydrometallurgical processes presents peculiar and difiicult problems inthat the resultant zinc calcine inherently contains impurities whicheither require separate treatment for removal of these impurities orplace a material cost burden on the recovery of zinc by thehydrometallurgical process. We have carried out extensiveexperimentation for the purpose of calcining zinc sulfide orescontaminated with iron to produce a Zinc calcine which is lower in theundesirable impurities namely, zinc sulfide, zinc sulfate and ferrites,thereby increasing the solubility of the zinc content of the calcine andincreasing the yield of recoverable Zinc. ln the course of ourinvestigation on calcination of zinc sulfide ores we found thatconditions which tended to minimize formation of one impurity had thereverse effect on other impurities. More specifically we found thatoxidation of zinc sulfide in air at relatively low temperatures resultedin zinc sulfate as the principal product rather than zinc oxide. Also wefound it necessary that adequate temperature level be maintained toeffect as complete desulphurization as possible which conditi-ons wouldindicate the need of high temperature and long time to accomplishcomplete roasting operation. On the other hand we found that the rate offormation of ferrite increases with temperature and time of Contact.Accordingly, we directed our efforts to calcination operation conditionswherein the temperature was sufiiciently high to effect substantiallycomplete desulphurization with minimum formation of zinc sulfate and thetime of contact low to retard ferrite formation. But even under theseconditions it was found that undesirable amounts of zinc sulfate wereformed. Further investigation showed that this deleterious effect tookplace outside of the calcination zone. Thus, it will be seen thatcalcination of zinc sulfide ores containing iron to produce a calcineparticularly suitable for a hydrometallurgical process is complicatedand dependent upon several factors.

In accordance with the present invention we have produced from zincsulfide ore containing iron a zinc calcine eminently suitable forhydrometallurgical process and containing only minor amounts of zincsulfide, zinc sulfate and ferrite with high solubility of the zinccontent of the calcine in leach liquor by maintaining at a temperaturewithin the range of l500-l650 F., preferably 1550- 1600 F. a fluidizedbed containing particles of partially roasted ore finer than about 100mesh size and particles of substantially completely roasted ore largerthan about 100 mesh size, introducing iron containing zinc sulfide orecontaining particles finer than about 100 mesh and coarser than about100 mesh into the fluidized bed at a point below the top surface of theiluidized bed and about 6 inches to 3 feet above the bottom surface ofthe bed, passing an oxygen containing gas, preferably air, in an amountat least sufficient to convert the sulfide ore to the correspondingoxide up through the bed to maintain the bed in fiuidized condition andto partially oxidize the feed sulfide ore and to entrain and carry outof the iiuidized bed partially roasted particles of ore finer than about100 mesh, introducing gas above the top surface of the iiuidized bed forcontrol of temperature in the free space above the bed, passing thesuspension of partially roasted feed ore in gas from the top of the bedinto a free space thereabove having a volume at least seven timespreferably -20 times the volume of the fluidized bed, passing thepartially roasted ore suspended in the gas through the free space toeffect substantially complete oxidation of the sulfide ore to thecorresponding oxide, maintaining the temperature of the free spacethereabove within the range of 1500-1800" F. preferably within the rangeof 1650-1750 F., discharging the substantially completely roasted oreand gas from the free space, separating the roasted ore particles fromthe gas i.e. at least about 75 percent preferably in excess of 90percent, while maintaining a temperature of at least 1450 F. preferablywithin the range of 1500-1700 F., prior to and during separation of theroasted ore particles from the gas, discharging the separated roastedparticles from the separator, thereafter cooling the gas c g. by a Wasteheat boiler and recovering the remainder of the tine particles of dustin the gas eg. by hot gas electrostatic precipitator. The temperature inthe fluid bed and the free space above it may be controlled by anysuitable cooling means, since the reaction is highly exothermic. Aconvenient method of controlling the temperature of the uid bed is bythe introduction of a liquid such as water or waste acid and thetemperature of the free space above the bed may be controlled byrecycling cooler gas or by spraying liquid in to the top of the reactionchamber or a combination of these methods.

The accompanying drawing diagrammatically illustrates one method ofcarrying out the operation of the present invention.

Referring to ore storage bin 1 in the drawing, zinc sulfide ores, thecharge to the process, used for production of metallic zinc are usuallyconcentrates which can range from about -95 percent finer than 100 meshwith the remainder generally coarser than 100 mesh and usually a maximumsize of about 1A inch. The zinc content will range from -55 percent andsulfur from about 27-36% or more. Iron may be present in quantitiesranging from about 1 percent to about 15-20 percent. Other impuritiessuch as copper, lead and cadmium may also be present. The ore feed frombin 1 passes down through line 2 and is fed by means of screw 3 directlyinto fluid bed 4 at a point below the upper surface of the fluid bed butata point of about 1/2-3 feet above the lower surface of the bed. TheHuid bed is supported on distributor plate S which may he a horizontalplate having perforations to permit the passage of air up through theplate. Bed 4 is composed of solid particles ranging from largerparticles of roasted ore up to about 1A inch size to tine particlesbelow mesh of partially roasted ore. Oxygen containing gas, preferablyair, for fluidizing and combustion is introduced by means of fan 6through line 7 into wind box 8 below distributor plate 5 and then passesupwardly through plate 5 and bed 4.

As the feed ore enters bed 4 at a point a short distance above thebottom of the bed it is partially roasted and the fine particles belowabout 100 mesh of partially roasted ore are swept out and carried intothe free space above the bed. The larger particles of ore above about100 mesh are retained in the bed where they are substantially completelyroasted. Complete oxidation of the finely divided ore particles in thefluid bed 4 need not be attempted. The temperature in the uid bed shouldbe at least 1500 F. and should not exceed 1650" F. Temperatures below()o F. were found to induce the formation of zinc sulfate andtemperatures above 1650u F. in the bed may cause localized hot spotswhich tend to increase ferrite formation. Since the reaction is highlyexothermic there is a tendency for the temperature to rise to anundesired height and water or Waste acid entering through line 9 may beintroduced in regulated amounts for controlling the bed temperature. Theair passes up through the bed 4 at a moderate velocity, about 21/2-31/2feet per second, sutiicient to fluidize the bed and carry the iineparticles above the bed. Extremely high velocities are undesirable asthey introduce excessive amounts of air which dilutes the concentrationof SO2 in the discharge gas. Also high velocity gas would entrain andcarry particles larger than about 100 mesh with possible loss oftiuidization. Roaster 11 is a Vertical chamber wherein the reactiontakes place with as previously described a distributor plate 5 near thebottom on which is supported a fluid bed 4 and above which is a freespace 12 wherein desulphurization is substantially completed. In ourinvestigation we found that the relative height of the free space 12compared to the height of the fluid bed 4 was important and to obtaingood results the free space should have a height at least 7 times theheight of the fluid bed preferably 10 to 20 times the height of thetiuid bed. Merely as i1- lustrative, a roaster 20 feet in diameter and50 feet high would have a height of iiuid bed of 5 feet and a free spaceabove the iuid bed or 45 feet or a ratio of 9:1. The entrained partiallyburned ore solids in the gas pass upwardly from the top of fluid bed 4through the free space 12 wherein oxidation continues. The temperaturein the free space 12 should be within the range of 1500- 1800 F. andpreferably within the range of l650-1750 F. Temperatures above 1800 F.favor ferrite formation and should be avoided. The temperature in freespace 12 should desirably be above 1650 F. to facilitate completedesulphurization and minimize zinc sulfide. The temperature in freespace 12 may be maintained higher than bed 4 because in free space 12the particles are in dispersed condition and undesirable localized hotspots will not occur whereas in bed 4 under such higher temperaturesthere will be such localized hot spots due to the close proximity of theparticles. The temperature in free space 12 may be regulated byintroduction of water or waste acid entering through line 13 or bycooled recycle gas entering roaster 11 through line 14. The gas enteringfree space 12 through line 14 serves to cool the free space and,particularly in View of the great height of the free space, aids incarrying the fine particles up through the free space and out of thereaction zone. Velocity of gas in the free space due to introduction ofadditional gas and/or liquid coolant there is appreciably higher than iniiuid bed 4 and is of the order of about 4-10 feet per second. Aspreviously mentioned the orc feed introduced into roaster 11 by means ofscrew 3 contains some larger size particles usually 5 to 25 percentwhich particles are too large to be entrained by the uprising airpassing through the bed and therefore accumulate in fluid bed 4. Thisaccumulation of roasted ore may be discharged from the bed by means ofscrew through line 1 6 either continuously or intermittently.

Gases and suspended roasted particles are released from the top ofroaster 11 through tine 1.7 which is insulated to minimize heat loss andtemperature drop, and then discharge into hot dust collector 18 whichmay be a centrifugalv dust collector of a conventional cyclone typewherein substantially all the solid particles usually 85-90 percent areseparated from the gases and discharged from the bottom of hot dustcollector 18 by means of screw 19 through line 21. It is most importantthat separation of the bulk of dust from the gases take place at a hightemperature, above 1450 F. and without prior cooling before and duringseparation to a temperature below 1450 F. or else the quality of theproduct will be appreciably deteriorated. To insure that the temperaturein the hot dust collector 18 remains above 1450 F. preferably at atemperature of 1500-1700 F., the dust collector may be heated externallyor be heavily insulated.

Gases substantially free of suspended solids but containing minor amountof tine dust discharge from the top of dust collector 1.8 through line22 where they are introduced into conventional waste heat boiler 23 forthe purpose of cooling the gases generally to a temperature about50G-700 F. and for utilizing the sensible heat in the gases to generatesteam in the waste heat boiler which is bled from the waste heat boilerthrough line 24. Any small amount of nes which deposit in waste heatboiler 23 may be discharged through line 25 and directed by means ofscrew 26 and line 27 to storage. The cooled gases released from Wasteheat boiler through line 28 are forced by means of fan 29 throughconventional hot gas electrostatic precipitator 31 to remove the lasttraces of tine particles of dust entrained in the gas which dust isdischarged through line 32, screw 33 and line 34. The purified cooledgas containing SO2 is directed via line 35 to conventional contactprocess for conversion to H2SO4. A portion of the cooled gas dischargingthrough line Z8 from waste heat boiler 23 may be returned by means offan 36 through line 14 to free space 12 of roaster 11. The calcinedischarging through lines 16, 21, 27 and 34 may be separately collectedor may be combined and pass through line 37 into cooler 38 wherein thecalcine is cooled to a temperature of about 200 F. and then directed vialine 39 to the leaching operation for the hydrometallurgical process.

The below examples illustrate the present invention.

Example I Zinc sulfide concentrates were burned in a roaster with aninside diameter of 5 feet and approximately 50i feet high with adistributor grate mounted in the base of the burner. Air for fluidizingand combustion was introduced into a wind box below the distributorplate through a iiue from a blower. Ore was introduced into the burnerat a single point 1 foot above the grate into a bed of prior roastedcalcine. A discharge outlet for periodic discharge of bed roastedcalcine was located about 14 inches above the distributor grate about180 from the ore inlet. Water for controlling bed temperature wasintroduced through a 1/2 inch pipe located 4 feet above the grate.Cooled recycled gas was introduced int-o the suspension zone through asingle 6 inch nozzle 9 feet 3 inches above the grate. Additional Waterfor suspension zone temperature control was introduced through a singlespray nozzle 12.5 feet above the grate.

Process gases and suspended calcined particles were removed from the topof the roaster through an insulated horizontal flue to an insulated dustcollector which had an efficiency of 85-95% with a 4 inch to 6 inch H2Opressure drop. The gases were piped to a waste heat boiler of aconventional sulfuric acid plant and through an electrostaticprecipitator, where remaining line suspended dust particles wereremoved. A portion of the cooled fd dust-free gases passed through ablower, and recycled back to the main burner for suspension zonetemperature control.

Calcines from the burner, dust collector and electrostatic precipitatorwere collected and weighed. They were then composited on a Weight basisfor subsequent leaching tests.

Using the above equipment, a zinc flotation concentrate assaying 50.2percent Zn, 13.4 percent Fe and 35.7 percent S dry basis, containing 2.8percent moisture, and 48.1 percent h325 mesh, percent -100 mesh and 10percent +100 mesh was fed into the burner at a rate of 22.3 lbs/minuteover an 18 hour period. Air Was fed up through the grate at the rate of905 s.c.f.m. into a 51 inch fluidized bed of 72#/c.f. density. Bedtemperature was maintained at 1575 F. by injection of 6# HZO/ minuteinto the iluid bed. Recycled gas at the rate of 200 c.f.m. wasintroduced into the suspension zone. Suspension zone temperatureincreased from 1575" F. 8 feet above the base plate to a maximum of 1730F. 29 feet and 1715 F. 45 feet above the base. Overall pressure dropthrough the 51 inch fluid bed was 135 inch H2O and 5.5 inch H2O throughthe dust collector.

4 percent of the resulting calcine was discharged from the fluid bed, 6percent from the electrostatic precipitator and the balance of 90percent from the hot dust collector. Composite calcine contained 60.2percent zinc, 16.4 percent Fe, 0.2 percent suliide sulfur, 0.6 percentsulfate sulfur and a ferritization ratio of 0.312. Soluble zinc asdetermined by a standard leach test was 55.1 percent or 91.4 percent oftotal zinc content. Free oxygen content of the discharge gas at burnerexit was 5.5 percent.

Example II In the same equipment as in Example I, zinc flotationconcentrate containing 55.0 percent Zn, 8.9 percent Fe and 33.4 percentS, dry basis, containing 6.6 precent moisture and 88.2 percent -325 meshpercent 100 mesh and 5 percent +100 mesh was fed into the burner at arate of 26.5#/rninute over a 28 hour period. Air was fed up through thegrate at the rate of 880 s.c.f.m. into a 45 inch uidized bed of 75#/c.f.density. Bed temperature was maintained at 1575 F. by injection of 3#H2O/minute into the bed. Recycle gas iiow was 490 s.c.f.rn. into thesuspension zone. Suspension zone temperatures were 1575 F. 8 feet abovethe grate, a maximum of 1725 F. at 29 feet above the grate and 1670o F.at the dust collector inlet. Overall pressure drop through the 45 inchbed was 125 inch H2O and 5.5 inch across the dust collector. Calcinedistribution was 4 percent from the bed, 6 percent from theelectrostatic pre-v cipitator and 90 percent from the dust collector.Composite calcine contained 65.9 percent total Zn, 61.8 percent solublezinc, 10.8 percent Fe, 0.10 percent suliide sulfur, 0.62 percent sulfatesulfur and a ferritization ratio of 0.380, with a leach eiiiciency of93.4 percent.

Although certain preferred embodiments of the invention have beendisclosed for purpose of illustration, it will be evident that variouschanges and modifications may be made therein without departing from thescope and spirit of the invention.

We claim:

l. A process for the production of zinc calcine characterized by lowferritization ratio, low zinc sulfide, low zinc sulfate and highsolubility of the zinc content of the calcine in leach liquor, whichcomprises maintaining at a temperature within the range of 1500-1650 F.a fluidized bed containing particles of partially roasted ore finer thanmesh and particles of substantially completely roasted ore larger than100 mesh, introducing iron containing zinc sulde ore containingparticles liner than 100 mesh and coarser than 100 mesh into theiiuidized bed at a point below the top surface of the fluidized bed andabout 1/2-3 feet above the bottom surface of the bed, passing an oxygencontaining gas in an amount at least suflicient to convert the sulfideore to the corresponding oxide up through the bed to maintain the bed infiuidized condition and to partially oxidize the feed sulfide ore and toentrain and carry out of the fiuidized bed partially roasted particlesof ore finer than about 100 mesh, passing the suspension of partiallyroasted feed ore in gas from the top of the bed into a free spacethereabove having a height at least seven times the height of thefluidized bed, passing the partially roasted ore suspended in the gasthrough the free space to effect substantially complete oxidation of thesulfide -ore to the corresponding oxide, maintaining the temperature ofthe free space thereabove within the range of l500-l800 F., dischargingthe substantially completely roasted ore and gas from the free space,separating roasted ore particles from the gas while maintaining atemperature of at least l450 F. prior to and during separation of theroasted ore particles from the gas, discharging the separated roastedparticles from the separator and discharging the gas from the separator.

2. A process for the production of zinc calcine characterized by loWferritization ratio, low zinc sulfide, low zinc sulfate and highsolubility of the zinc content of the calcine in leach liquor, whichcomprises maintaining at a temperature within the range of 1550-1600 F.a fiuidized bed containing particles of partially roasted ore finer than100 mesh and particles of substantially cornpletely roasted ore largerthan 100 mesh, introducing iron containing Zinc sulfide ore containingparticles finer than 100 mesh and coarser than 100 mesh into thefluidized bed at a point below the top surface of the fluidized bed andabout 1/z--3 feet above the bottom surface of the bed, passing an oxygencontaining gas in an amount at least sufficient to convert the sulfideore to the corresponding oxide up through the bed to maintain the bed infiuidized condition and to partially oxidize the feed sulfide ore and toentrain and carry out of the fluidized bed partially roasted particlesof ore finer than about 100 mesh, introducing recycled cooled gas abovethe top surface of the fluidized bed, passing the suspension ofpartially roasted feed ore in gas from the top of the bed into a freespace thereabove having a height ten to twenty times the height of thefiuidized bed, passing the partially roasted ore suspended in the gasthrough the free space to effect substantially complete oxidation of thesulfide ore to the corresponding oxide, maintaining the temperature ofthe free space thereabove within the range of 160Q-1750" F., dischargingthe substantially completely roasted ore and gas from the free space,separating roasted ore particles from the gas while maintaining atemperature of 1500- 1700" F. prior to and during separation of theroasted ore particles from the gas, discharging the separated roastedparticles from the separator and discharging the gas from the separator.

3. A process for the production of zinc calcine characterized by lowferritization ratio, low zinc sulfide, low zinc sulfate and highsolubility of the zinc content of the calcine in leach liquor, whichcomprises maintaining at a temperature Within the range of l550-1600 F.a fluidized bed containing particles of partially roasted ore finer than100 mesh and particles of substantially completely roasted ore largerthan 100 mesh, introducing iron containing zinc sulfide ore containingparticles finer than 100 mesh and coarser than 100 mesh into thefluidized bed at a point below the top surface of the fiuidized bed andabout 1/2-3 feet above the bottom surface of the bed, passing an oxygencontaining gas in an amount at least sufiicient to convert the sulfideore to the corresponding oxide up through the be-d to maintain the bedin fluidized condition and to partially oxidize the feed sulfide ore andto entrain and carry out of the fluidized bed partially roastedparticles of ore finer than about 100 mesh, passing the suspension ofpartially roasted feed ore in gas from the top of the bed into a freespace thereabove having a height ten to twenty times the height of thefiuidized bed, passing the partially roasted ore suspended in the gasthrough the free space to effect substantially complete oxidation of thesulfide ore to the corresponding oxide, maintaining the temperature ofthe free space thereabove within the range of 1600-1750 F., controllingthe temperature of the fluid bed by the introduction of water directlyinto the uid bed and the temperature of the free space above the bed byrecycling cooler gas into the free space, discharging the substantiallycompletely roasted ore and gas from the free space, separating at leastpercent of the roasted ore particles from the gas while maintaining atemperature Within the range of about 1500-1700 F. prior to and duringseparation of the roasted ore particles from the gas, discharging theseparated roasted particles from the separator, and discharging the gasfrom the separator.

4. A process for the production of zinc calcine characterized by lowferritization ratio, low zinc sulde, low zinc sulfate and highsolubility of the zinc content of the calcine in leach liquor, whichcomprises maintaining at a temperature within the range of 1550-1600 F.a fluidized bed containing particles of partially roasted ore finer thanmesh and particles of substantially completely roasted ore larger than100 mesh, introducing iron containing zinc sulfide ore containingparticles finer than 100 mesh and coarser than 100 mesh into thefiuidized bed at a point below the top surface of the fiuidized bed andabout 1/2-3 feet above the bottom surface of the bed, passing an oxygencontaining gas in an amount at least sufiicient to convert the sulfideore to the corresponding oxide up through the bed to maintain the bed infiuidized condition and to partially oxidize the feed sulfide ore and toentrain and carry out of the fluidized bed partially roasted particlesof ore finer than about 100 mesh, passing the suspension of partiallyroasted feed ore in gas from the top of the bed into a free spacethereabove having a height ten to twenty times the height of thefiuidized bed, passing the partially roasted ore suspended in the gasthrough the free space to effect substantially complete oxidation of thesulfide ore to the corresponding oxide, maintaining the temperature ofthe free space thereabove Within the range of Q-1750 F., controlling thetemperature of the fluid bed by the introduction of water directly intothe fluid bed and the temperature of the free space above the bed byrecycling cooler gas into the free space, discharging the substantiallycompletely roasted ore and gas from the free space, separating at least90 percent of the roasted ore particles from the gas while maintaining atemperature Within the range of about 1500-1700 F. prior to and duringseparation of the roasted ore particles from the gas, discharging theseparated roasted 'particles from the separator, discharging the gasfrom the separator, cooling the gas by passing it through a waste heatboiler, and recovering the remainder of the fine particles of dust inthe gas by passing it through an electrostatic precipitator.

References Cited by the Examiner UNITED STATES PATENTS 2,847,294 8/58Long et al. 75-9 2,855,288 10/58 Cyr et al. 75-9 3,047,365 7/62 Julrkola75-9 FOREIGN PATENTS 482,962v 5/5'2 Canada. 645,977 1l/50 Great Britain.

BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner.

1. A PROCESS FOR THE PRODUCTION OF ZINC CALCINE CHARACTERIZED BY LOWFERRITIZATION RATIO, LOW ZINC SULFIDE, LOW ZINC SULFATE AND HIGHSOLUBILITY OF THE ZINC CONTENT OF THE CALCINE IN LEACH LIQUOR, WHICHCOMPRISES MAINTAINING AT A TEMPERATURE WITHIN THE RANGE OF 1500-1650*F.A FLUIDIZED BED CONTAINING PARTICLES OF PARTIALLY ROASTED ORE FINER THAN100 MESH AND PARTICLES OF SUBSTANTIALLY COMPLETELY ROASTED ORE LARGERTHAN 100 MESH, INTRODUCING IRON CONTAINING ZINC SULFIDE ORE CONTAININGPARTICLES FINER THAN 100 MESH AND COARSER THAN 100 MESH INTO THEFLUIDIZED BED AT A POINT BELOW THE TOP SURFACE OF THE FLUIDIZED BED ANDABOUT 1/2-3 FEET ABOVE THE BOTTOM SURFACE OF THE BED, PASSING AN OXYGENCONTAINING GAS IN AN AMOUNT AT LEAST SUFFICIENT TO CONVERT THE SULFIDEORE TO THE CORRESPONDING OXIDE UP THROUGH THE BED TO MAINTAIN THE BED INFLUIDIZED CONDITION AND TO PARTIALLY OXIDIZE THE FEED SULFIDE ORE AND TOENTRAIN AND CARRY OUT OF THE FLUIDIZED BED PARTIALLY ROASTED PARTICLESOF ORE FINER THAN ABOUT 100 MESH, PASSING THE SUSPENSION OF PARTIALLYROASTED FEED ORE IN GAS FROM THE TOP OF THE BED INTO A FREE SPACETHEREABOVE HAVING A HEIGHT AT LEAST SEVEN TIMES THE HEIGHT OF THEFLUIDIZED BED, PASSING THE PARTIALLY ROASTED ORE SUSPENDED IN THE GASTHROUGH THE FREE SPACE TO EFFECT SUBSTANTIALLY COMPLETE OXIDATION OF THESULFIDE ORE TO THE CORRESPONDING OXIDE, MAINTAINING THE TEMPERATURE OFTHE FREE SPACE THEREABOVE WITHIN THE RANGE OF 1500-1800*F., DISCHARGINGTHE SUBSTANTIALLY COMPLETELY ROASTED ORE AND GAS FROM THE FREE SPACE,SEPARATING ROASTED ORE PARTICLES FROM THE GAS WHILE MAINTAINING ATEMPERATURE OF AT LEAST 1450*F. PRIOR TO AND DURING SEPARATION OF THEROASTED ORE PARTICLES FROM THE GAS, DISCHARGING THE SEPARATED ROASTEDPARTICLES FROM THE SEPARATOR AND DISCHARGING THE GAS FROM THE SEPARATOR.